Question

我有2个表（SQL Server 2008）：Documents and Fields。

文件：

Id  (PK)
Some-Others-Columns

字段：

Id  (PK) 
DocumentId  (FK to Documents) 
Name
Value

每个文档都分配了80多个字段。我必须选择一个表，其中每一行都是一个文档+一些特定的字段（不是80+，只有一些字段）。

我的T-SQL代码对大表的工作速度非常慢，我该如何优化呢？

SELECT f1.Value AS 'f1', f2.Value AS 'f2', f3.Value AS 'f3', f4.Value AS 'f4', f5.Value AS 'f5', f6.Value AS 'f6', d.PartyId, d.CreationDate
FROM dbo.Fields AS f WITH (NOLOCK) 
  INNER JOIN dbo.Fields AS f1 ON f.Id = f1.Id 
  INNER JOIN dbo.Documents AS d ON f1.DocumentId = d.Id 
  INNER JOIN dbo.Fields AS f2 ON d.Id = f2.DocumentId
  INNER JOIN dbo.Fields AS f3 ON d.Id = f3.DocumentId
  INNER JOIN dbo.Fields AS f4 ON d.Id = f4.DocumentId
  INNER JOIN dbo.Fields AS f5 ON d.Id = f5.DocumentId
  INNER JOIN dbo.Fields AS f6 ON d.Id = f6.DocumentId

WHERE
    (f1.Name = 'Some-Name-1')
AND (f2.Name = 'Some-Name-2')
AND (f3.Name = 'Some-Name-3')
AND (f4.Name = 'Some-Name-4')
AND (f5.Name = 'Some-Name-5')
AND (f6.Name = 'Some-Name-6')

请帮助我优化此查询

Answer 1

不确定枢轴是否会表现更好，您需要将其与文档连接起来以获取其他文档字段。我的语法可能有点偏离（如果您希望我修复它，您可以设置一个SQL小提琴，其中插入了两个表和示例行：http://sqlfiddle.com/）

SELECT DocumentId, 
[Some-Name-1], [Some-Name-2], [Some-Name-3], [Some-Name-4], [Some-Name-5],[Some-Name-6]
FROM (
  Select f.DocumentId, f.Name, f.Value
  FROM dbo.Fields AS f 
  INNER JOIN dbo.Documents AS d ON f.DocumentId = d.Id ) as SourceTable
PIVOT
(
  SUM(Value)
  FOR Name IN ([Some-Name-1], [Some-Name-2], [Some-Name-3], [Some-Name-4], [Some-Name-5],[Some-Name-6])
) AS PivotTable;

Answer 2

您可以使用ctrl + l查看执行计划以及执行时间最长的内容。您很可能希望在字段表的ID和名称索引以及文档表上的ID

Answer 3

高性能成本来自于拥有如此多的连接。为什么不获取所需文档的“字段”的记录集？也许我没弄错......

SELECT value 
FROM Documents AS d 
INNER JOIN Fields as f ON d.Id=f.DocumentId 
WHERE (f.Name="Name1" or f.Name="Name2" or.. etc);

你应该在Document

的字段中拥有所有“Value”列的记录集

如果您需要形成列的值，则应在第一次查询后执行此操作

Answer 4

试试这个：

SELECT f1.Value AS 'f1', f2.Value AS 'f2', f3.Value AS 'f3', f4.Value AS 'f4', f5.Value AS 'f5', f6.Value AS 'f6', d.PartyId, d.CreationDate
FROM dbo.Fields AS f WITH (NOLOCK) 
INNER JOIN (SELECT Id, DocumentId, Value FROM dbo.Fields WHERE Name='Some-Name-1') AS f1 
    ON f.Id = f1.Id 
INNER JOIN (SELECT Id, CreationDate, PartyId  FROM dbo.Documents) AS d
    ON f1.DocumentId = d.Id 
INNER JOIN (SELECT Id, DocumentId, Value FROM dbo.Fields WHERE Name='Some-Name-2') AS f2
    ON d.Id = f2.DocumentId
INNER JOIN (SELECT Id, DocumentId, Value FROM dbo.Fields WHERE Name='Some-Name-3') AS f3
    ON d.Id = f3.DocumentId
INNER JOIN (SELECT Id, DocumentId, Value FROM dbo.Fields WHERE Name='Some-Name-4') AS f4
    ON d.Id = f4.DocumentId
INNER JOIN (SELECT Id, DocumentId, Value FROM dbo.Fields WHERE Name='Some-Name-5') AS f5
    ON d.Id = f5.DocumentId
INNER JOIN (SELECT Id, DocumentId, Value FROM dbo.Fields WHERE Name='Some-Name-6') AS f6
    ON d.Id = f6.DocumentId

如何优化多个内连接

4 个答案: